1. Field of the Invention
The present invention relates to an intake system of an outboard motor.
2. Description of the Related Art
An intake system of an outboard motor is generally disposed in a space defined between an engine and an engine cover which covers the engine.
Japanese Unexamined Patent Laid-open (KOKAI) Publication No. 2002-195118 discloses an outboard motor including intake pipes of different lengths in order to improve torque characteristics in the entire engine revolution range, from a low engine revolution range to a high engine revolution range. A switching operation to the intake pipes is performed according to operation condition of the engine.
That is, it is designed that, in a low-intermediate engine revolution range, the longer intake pipe is selected, and in the high revolution range, the shorter intake pipe is selected.
However, since the space between the engine and the engine cover is narrow, it is difficult to arrange therein the intake pipes of different lengths. Especially, since the intake pipe for the low-intermediate revolution range needs to be long, the arrangement thereof can be specifically restricted by the shape or size of the engine. Therefore, it is difficult to design the entire engine compactly.
In addition, although, in an arrangement in which an engine cover having an expanded size is utilized, the space for placing the intake pipes may be ensured, in a case of a large-displacement engine, there is a limit in the size of the engine cover according to the prescribed standard when mounting an outboard motor to a boat.
Furthermore, in the case of the large-displacement engine, the engine requires itself a long length from the front side to the rear side of the engine, and therefore, even if the intake pipe for the low-intermediate revolution range having an appropriate length is utilized, there is a possibility that a switching valve for switching from/to the intake pipe for the high revolution range is to be arranged to a side portion of the engine. In such case, the shape of the intake pipe for the low-intermediate revolution range is especially affected by the shape or size of the engine.